The Tumor Necrosis Factor (TNF) superfamily of cytokines and receptors play critical roles in development of the immune system, and in innate and acquired immune defenses to pathogens. LIGHT, an integral member of the lymphotoxin (LT)-alpha, LT beta, and TNF cytokine superfamily, signals through the Herpesvirus entry mediator (HVEM) and the LT betaR, a receptor that also binds membrane Lt alpha beta complex. Membrane Lt alpha beta is required for the development of the progenitors of natural killer (NK) and NK-T cell lineage. Ligands that engage the LT betaR, including LIGHT and LTalpha1 beta2, activate a potent non-apoptotic, antiviral response that suppresses spread of human cytomegalovirus (HCMV) in cell culture. Furthermore, LTalpha deficient mice exhibit a profound and specific susceptibility to acute infection with mouse CMV (MCMV), implicating the LT betaR as a key signaling element for host defense. The developmental connection between NKJNK-T cells and LT alpha beta provides compelling evidence that the antiviral activity of LT alpha beta/LIGHT is mediated by NK or NK-T cells and suggests that lymphotoxins are intimately linked to viral defenses. The antiviral signaling by the LTBR is hypothesized to provide a key checkpoint in limiting virus spread. The three specific aims are proposed to address this hypothesis. The first aim will use defined mutants of the LT betaR to identify receptor signaling complex, which leads to the anti-viral response observed in primary fibroblasts. Dominant negative mutants of TRAFs and death domain adaptors, known to bifurcate the signaling pathways at the receptor level, will be used in tissue culture models to determine the role that NFkappaB, JNK, and IRF signaling pathways contribute to the anti-HCMV activity. The second aim is directed at delineating the signaling pathways leading to LT alpha beta/LIGHT induction of interferon (IFN)beta in HCMV infected cells. Additionally, in order to dissect the mechanism of cytokine anti-viral effects, DNA microarray technology will be used to analyze differences in HCMV gene expression in the presence of Ltalpha beta/LIGHT and IFNB. The third aim will address the physiologic role of LT alpha beta and LIGHT in regulating innate and immune defense to MCMV using: genetically defined mice deficient in LTcx/13 and LIGHT systems, transgenic mice expressing decoy receptors, and pharmacological modulation by receptor specific monoclonal antibodies and purified soluble decoy receptors. MCMV models of acute infection and reactivation will be investigated. Together these studies will provide a comprehensive investigation into anti-CMV actions of the LT alpha beta/LIGHT cytokine systems in human and mouse models that will elucidate molecular mechanisms of host-pathogen interactions that occur during acute and persistent infections.